Annealing of polymers

The macroscopic thermal analysis, furthermore, proves that it is also common for melting of the original crystals to be followed by recrystallization to a more stable morphology. Finally, some crystals may have different crystal structures at high temperatures and, thus, show polymorphic transitions on annealing. Annealing of polymers to a more stable state as shown in Fig. 6.79, simply expressed by a decrease in free enthalpy, may thus be a rather complicated process (compare to Sect. 2.4.2). 

In the discussion following a brief account will be given on techniques of rapid quenching and annealing of polymers. 

This is a fairly reasonable way to describe man-made amorphous polymers, which had not been given time to anneal. For polymers that form very quickly, a quick Monte Carlo search on addition can insert an amount of nonoptimal randomness, as is expected in the physical system. 

In numerous applications of polymeric materials multilayers of films are used. This practice is found in microelectronic, aeronautical, and biomedical applications to name a few. Developing good adhesion between these layers requires interdiffusion of the molecules at the interfaces between the layers over size scales comparable to the molecular diameter (tens of nm). In addition, these interfaces are buried within the specimen. Aside from this practical aspect, interdififlision over short distances holds the key for critically evaluating current theories of polymer difllision. Theories of polymer interdiffusion predict specific shapes for the concentration profile of segments across the interface as a function of time. Interdiffiision studies on bilayered specimen comprised of a layer of polystyrene (PS) on a layer of perdeuterated (PS) d-PS, can be used as a model system that will capture the fundamental physics of the problem. Initially, the bilayer will have a sharp interface, which upon annealing will broaden with time. 

Polymer-polymer fractal interfaces may result from the interdiffusion of monomers or of polymers themselves. Koizumi et al. [31] annealed the interface between polystyrene and a styrene-isoprene diblock polymer at 150 C and showed extensive roughening of the interface by mutual interdiffusion on a micron scale (Fig. 8). 

A very specific surface structure is observed after the annealing of a PS/polybuta-diene (PB) diblock copolymer, PS-b-PB, shown in Fig. 7 b. The surface is very smooth directly after preparation of the film from solution (similar to Fig. 7 a). By annealing at 120 °C the surface structure shown in Fig. 7 b evolves, which we believe is due to the formation of layers of PS and PB parallel to the surface. The outermost layer might not be completely filled due to lack of material leading to steps at the surface. Similar behavior is observed with other diblock copolymers such as PS-b-PMMA [61]. Enrichment of one component is also observed at the surface of a polymer solution [115,116] by X-ray fluorescene and evanescent wave techniques. 

IC Sanchez. Theory of polymer crystal thickening during annealing. J Appl Phys 45 4216-4219, 1974. 

We have speculated that when the melt is kept above the melting temperature, ve gradually increases with an increase of At and approaches the equilibrium ve (ve = 1). It was shown that the melt relaxation process takes a long time, i.e., it takes several hours or a few days depending on the annealing temperature (Tmax) and Mn. However, this experimental fact was indirect evidence of the role of entanglement in the nucleation of polymers. 

Since the possibility of direct melt intercalation was first demonstrated [11], melt intercalation has become a method of preparation of the intercalated polymer/ layered silicate nanocomposites (PLSNCs). This process involves annealing, statically or under shear, a mixture of the polymer and organically modified layered fillers (OMLFs) above the softening point of the polymer. During annealing, the polymer chains diffused from the bulk polymer melt into the nano-galleries between the layered fillers. 

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